The actions at demo.bpmn.io
use Modeler APIs, but the buttons themselves are not part of the library. You can create your own buttons in your project and add event handlers to them, e.g.
template:
<button (click)="zoomIn()">zoom in</button>
in the component
// component method
public zoomIn() {
this.BpmnJS.get('zoomScroll').stepZoom(1);
}